The phrase ballasted railroad track refers to railroad track that consists of steel rails mounted on top of support beams called ties that are perpendicular to the rails and that in turn rest on and are surrounded by a bed of small rocks called ballast. A bed of track ballast tends to change shape with time due to its lack of rigidity, due to settlement of the earth on which it rests, due to strains within the rails, and due to forces applied to the rails by passing railroad vehicles. As a result the shape of the guidance path provided by the rails tends to change and degrade with time, and maintenance needs to be performed from time to time to restore the shape of the rails. Such maintenance work is now normally performed using a large semi-automated tamping machine that is able under computer control to adjust the location of a few ties at a time (and the portions of rail that are attached to those ties) while agitating the ballast so that the ties are easier to move and so that the ballast tends to fill in around the adjusted tie locations. This invention has to do with the way that instructions for controlling the operation of such a tamper are computed.
Prior art relating to tamping ballasted railroad track is extensive. Here attention is limited to methods for calculating the lateral displacements between current and desired locations of points along a track. Such displacements are sometimes referred to as track throws.
Prior calculation of corrections to the horizontal geometry of a section of track was based on calculation of a desired location along the track for the start of each transition from tangent or circular arc to spiral and from spiral to another circular arc or back to tangent. Typically a computer program that an engineer or tamper operator uses for calculation of tamping instructions will analyze recently made measurements of track shape to estimate the locations for those transition points, may allow the engineer or operator to adjust them, and will then calculate tamping instructions aimed at bringing the track shape closer to a form with transition points as specified. See, for example, U.S. Pat. No. 5,012,413, entitled “Railroad track curve lining apparatus and method”.